A Royal Caribbean cruise ship returned to port early as an outbreak of norovirus caused 577 of the passengers (out of 3050 on board) and 49 of the crew to become ill.
Symptoms of norovirus infection include vomiting and diarrhea as well as nausea, stomach pains, headache, fever, and body pain. The symptoms can last from one to several days. The vomiting can often be described as acute onset vomiting, which means that as soon as you feel like you have to vomit, you vomit...and that can be anywhere you are standing or sitting, including the dinner table. This is one reason it can be spread so easily within a captive group of people, such as on a cruise ship. The virus can be aerosolized on the vomitus particles as it leaves the person's mouth
Another reason is that the virus is stable on surfaces unless that surface is effectively sanitized. So it can get onto people's hands, onto food, onto dinner tables, and unless properly cleaned and sanitized, it will remain there until it is transferred to another's hands or to a food item.
People can continue to shed the virus even after the symptoms have subsided. So hand washing continues to be a must.
The cruise ship industry has gone to great measures to prevent such outbreaks. Constant cleaning and quarantining sick people are standard practices. However once the illness gets to a critical mass, it can be next to impossible to control, and that is what appears to have happened here.
This cruise ship will need to undergo extensive cleaning and sanitizing before returning to service. Residual virus-containing vomit not cleaned can serve as the source for the next outbreak. And with that many people reported as being ill, you can imagine the amount of yuck laying around the place.